Final answer:
A vessel restricted in its ability to manoeuvre and engaged in underwater operations with an obstruction, when not making way, must display three all-round lights in a vertical line with the top and bottom lights being red and the middle light being white. If at anchor, it must display the appropriate lights or shapes for vessels at anchor to notify other vessels to navigate cautiously around them.
Step-by-step explanation:
The question pertains to the navigation lights and shapes required for a vessel that is restricted in ability to manoeuvre (RAM), specifically one that is engaged in underwater operations with an obstruction and not making way through the water. For such a vessel, the international regulations, as per the International Regulations for Preventing Collisions at Sea (COLREGs), specify that it must display:
- Three all-round lights in a vertical line where the highest and lowest are red and the middle is white;
- If making way, three shapes in a vertical line where the highest and lowest are balls and the middle one is a diamond;
- If at anchor, the vessel should also display lights or shapes prescribed for vessels at anchor.
These lights and shapes serve to inform other vessels of the vessel's restricted manoeuvrability and that they should navigate with extreme caution when near it. The regulations ensure safety on the waters by providing clear, visible cues to others in the vicinity.